KR20020026441A - Radio communication system with adjustment of the output power of a transmitting station - Google Patents

Abstract

A radio communication system comprising one first station and a plurality of second stations has a communication channel for transmitting information from the second station to the first station. The second station may adjust its output power in response to a power control command received from the second station and adjust its output transmit power at a plurality of different ratios. The first station may instruct the second station what proportion of the plurality it should use. The first station determines an optimum ratio for the second station to use by analyzing a sequence of power control commands sent to the second station, and instructs the second station accordingly.

Description

RADIO COMMUNICATION SYSTEM WITH ADJUSTMENT OF THE OUTPUT POWER OF A TRANSMITTING STATION

There are two basic types of communication required between a base station (BS) and a mobile station (MS) in a wireless communication system. The first is user traffic, for example voice or packet data. Second is control information necessary to set and monitor various parameters of the transmission channel to enable the BS and MS to exchange the necessary user traffic.

In many communication systems, one of the functions of the control information is to enable power control. Power control of the signal transmitted from the MS to the BS is required in order to minimize the transmit power required by each MS while the BS receives signals from each different MS at approximately the same power level. Power control of the signal transmitted by the BS to the MS is required, in order to reduce interference with other cells and radio systems, while the MS receives the signal from the BS at a low error rate, while minimizing the transmit power To do that. In a two-way radio communication system, power control can be operated in a closed loop or open loop method. In a closed loop system, the MS determines the necessary change in transmit power from the BS, signals this change to the BS, and vice versa. In an open loop system that can be used in a TDD system, the MS measures the signal received from the BS and uses this measurement to determine the necessary change in transmit power.

An example of a combined time and frequency division multiple access system using power control is the Global System for Mobile communication (GSM), where the transmit power of both BS and MS transmitters is controlled in 2 dB steps. do. Similarly, power control implementations in systems using Spread Spectrum Code Division Multiple Access (CDMA) technology are disclosed in US patent (US-A-5 056 109).

In considering closed loop power control, we know that for any given channel condition, there is an optimal power control step size that minimizes the E _b / N _O (energy / noise density per bit) needed to achieve a particular bit error rate. Can be. When the channel changes very slowly, the optimal step size may be less than 1 dB, because such values are sufficient to track changes in the channel while providing minimal tracking error. As the Doppler frequency increases (but generally not only because of the movement of the MS), larger step sizes provide better performance with optimum values exceeding 2 dB. However, as the Doppler frequency increases further, the latency (or update rate) of the power control loop becomes so large that the channel cannot be properly tracked, and the point where the optimum step size decreases again, perhaps below 0.5 dB. Leads to The reason is that fast channel changes cannot be tracked, so the ability to follow shadowing is needed, which generally slows down processing.

Since the optimal power control step size can change dynamically, performance can be improved when the BS informs the MS which value of the power control step size should be used for the uplink transmission to the BS. One example of a system using such a method is the UMTS Frequency Division Duplex (FDD) standard, where power control is important because of the use of CDMA technology.

A problem in a communication system with variable power control step size is how to ensure that the step size remains set to an optimal value. Although the optimal step size for a particular MS speed is known, the MS generally does not know its speed. Moreover, the MS itself speed is not the only factor that actually affects the optimal power control step size.

The present invention relates to a radio communication system, and further relates to a second station for use in such a system and a method of operating such a system. Although the present disclosure describes a system that is of particular relevance to the recent Universal Mobile Telecommunication System (UMTS), it can be seen that such techniques are equally applicable for use in other mobile radio systems.

1 is a schematic block diagram of a radio communication system.

2 is a graph of the speed of an MS versus the optimal power control step size.

3 illustrates a possible transition between power control states in a UMTS system.

4 is a flow diagram illustrating a method according to the invention for adjusting power control parameters.

It is an object of the present invention to address the problem of dynamically selecting an optimal power control step size.

According to a first aspect of the present invention, a radio having a communication channel between a first station and a second station for transmitting information from one of the first station and the second station (the transmitting station) to another station (the receiving station). A communication system is provided, wherein the transmitting station has means for adjusting its output power at a plurality of different rates, the receiving station having to adjust the transmission strength of the signal received from the transmitting station. Means for determining whether or not, to transmit a power control command to the transmitting station to instruct the transmitting station to adjust its output power, and to determine the output power of the transmitting station from the sequence of power control commands sent to the transmitting station. Means for determining an appropriate adjustment rate, and means for delivering the adjustment rate to a transmitting station; The station has means for responding to the communication from the receiving station to set its rate of adjustment of its output power.

The different adjustment rate of the output power can be changed by changing the output power at predetermined intervals by steps of different magnitudes, by changing the output power at intervals changed by steps of predetermined magnitudes, or by some combination of the two techniques. Can be achieved. The small power control step size can be emulated, for example, by changing only the output power when a certain number of identical power control commands have been received.

According to a second aspect of the present invention, there is provided a first station for use in a radio communication system having a communication channel between a first station and a second station, the second station having its output power at a plurality of different ratios. Means for adjusting how the transmission strength of a signal received from the second station should be adjusted, and for instructing the second station to adjust its output power. Means for sending a power control command to the second station, means for determining an appropriate rate of adjustment of the output power of the second station from the sequence of power control commands sent to the second station, and transmitting the rate of adjustment to the second station. Means for providing are provided.

According to a third aspect of the present invention, there is provided a second station for use in a radio communication system having a communication channel between a second station and a first station, the first station having its output power at a plurality of different ratios. Means for adjusting how the transmission strength of a signal received from the first station should be adjusted, and for instructing the first station to adjust its output power. Means for sending a power control command to the first station, means for determining an appropriate rate of adjustment of the output power of the first station from a sequence of power control commands sent to the first station, and transmitting the rate of adjustment to the first station. Means for providing are provided.

According to a fourth aspect of the present invention, a radio communication is provided with a communication channel between a first station and a second station for transmitting information from one of the first station and the second station (the sending station) to another station (the receiving station). A method of operating a system is provided, wherein the transmitting station can adjust its output power at a plurality of different ratios, the method determining how the receiving station should adjust the transmission strength of a signal received from the transmitting station. Determining the appropriate adjustment rate of the output power of the transmitting station from the sequence of power control commands sent to the transmitting station, and sending a power control command to the transmitting station to instruct the transmitting station to adjust its output power. Transmitting the adjustment rate to a transmitting station, and in response, the transmitting station transmits its output power. And a step of setting the update ratio.

The present invention, although not provided in the prior art, is based on the recognition that the optimal power control step size can be determined from the characteristics of the transmitted power control command.

Embodiments of the invention will now be described with reference to the accompanying drawings by way of example.

Referring to FIG. 1, a radio communication system includes one first station (BS) 100 and a plurality of second stations (MS) 110. BS 100 is a microcontroller (μC) 102, transceiver means (Tx / Rx) 104 connected to radio transmitting means 106, and power control means (PC) 107 for changing the transmitted power level. And connection means 108 for connecting to the PSTN or other suitable network. Each MS 110 includes a microcontroller (μC) 112, a transceiver means (Tx / Rx) 114 connected to a radio transmitting means 116, and a power control means (PC) for changing the transmitted power level. 118; Communication from BS 100 to MS 110 occurs on downlink channel 122, while communication from MS 110 to BS 100 occurs on uplink channel 124.

In the presently described UMTS system, the purpose of uplink power control is to instruct the MS 110 to change its transmit power so that the signal-to-interference ratio (SIR) of the signal received by the BS 100 at a certain target level. It is to maintain Signal-to-Interference Ratio. This indication is conveyed by a two-state Transmit Power Control (TPC) command that is transmitted once per time slot (which results in 15 time slots per 10 ms frame). The step size is divided into two parameters: power control algorithm (PCA) and (Uplink transmit power control step size), which results in the availability of three active power control step sizes.

When the value of PCA is 1, Can take a value of 1 or 2. If the received TPC command is "0", the MS 110 returns its transmit power. While decreasing by dB, if the received command is "1", the MS 110 reduces its transmit power. Increment by dB

When the value of PCA is 2, Can only take a value of 1, and the MS 110 combines the TPC commands into a group of five commands. If all five TPC commands are "1", then the transmit power is If increasing by dB and all five TPC commands are "0", then the transmit power is Reduced by dB, otherwise the transmit power does not change. This method effectively emulates the use of a power control step size of approximately 0.2 dB as disclosed in British Patent Application No. 9915571.5 (Our Control Number PHB 34358).

2 is a graph showing how the optimal power control step size changes for the speed of the MS 110 over a range of 3 to 300 km / h. Data for the graph is obtained from simulations to determine the step size needed to minimize the value of E _b / N ₀ required for a bit error rate of 0.01. Simulation makes a number of ideal assumptions such as:

There is one slot delay in the power control loop;

No channel coding;

There is perfect channel estimation by the receiver;

Equalization at the receiver is performed by a complete RAKE receiver;

There is a fixed error rate in the transmission of power control commands;

The channel model is an existing multipath Rayleigh UMTS channel (for example ITU pedestal-A channel);

All changes in the radio channel are due to the movement of the MS 110.

The graph shows that the best results are obtained with a small power control step size over a channel that changes relatively slowly at low speeds. As the speed of the MS increases, the optimal step size also increases as expected because the channel is changing faster. However, for speeds above about 60 km / h, the optimum step size decreases again. This is because the rate of change of the channel is higher than can be tracked assuming the update rate of the inner loop power control. In such an environment, due to shadowing, for example, optimal operation is obtained by ignoring rapid fluctuations and instead only tracking relatively slow changes in average channel attenuation, thus using a small power control step size. This is done.

For basic inner loop power control in a UMTS system, BS 100 measures the value of the received SIR every time slot (although this measurement may be made somewhat frequently). If the received SIR is greater than the target level, the next TPC command sent by the BS 100 to the MS 110 is "0" (instructing the MS 100 to reduce its transmit power), If not larger, then the TPC command is "1" (instructing MS 110 to increase its transmit power).

In one embodiment of the system made in accordance with the present invention, the analysis of the statistical properties of the sequence of TPC commands sent to the MS 110 is performed by the PCA and the PCA. It is used to determine the most appropriate setting for the parameter. Consider an overview of some examples:

The regularly crossing sequence of TPC commands indicates that the SIR of the signal on the uplink channel 124 remains very close to the SIR threshold, Setting to 1 indicates a very slowly changing radio channel that is appropriate.

The same sequence of TPC commands indicates that the uplink channel 124 is changing faster, from which also the PCA to 1 It can be inferred that setting to 1 or 2 will provide the best performance.

Apparently a random sequence of TPC commands indicates that the rate of change of uplink channel 124 is greater than the rate of update of the inner loop power control. In such an environment, PCA to 2 also Setting to 1 will provide optimal performance as described above in connection with the graph of FIG. 2.

Further statistical analysis of the transmitted TPC commands is also possible in addition to or instead of the above example, the proposed PCA and Can be used to influence the choice of. Suitable parameters for analysis may include:

Average net requested change in uplink power, determined over a fixed or sliding time period, and

A time-weighted average change in the requested uplink power, determined over a fixed or changing time period, for example the most recent change may be assigned a higher weight than the earlier change.

For example, one of these parameters may be repeatedly calculated and updated for each time slot using the most recent TPC command value.

As shown in FIG. 3, according to the sequence of TPC commands, PCA and A transition can be made between any three possible combinations of parameters. For example, the initial setting may be the setting of state 302, where PCA is 1, Is set to two. Then, the BS 100 can determine that a TPC command that intersects regularly is being transmitted, so that the PCA is equal to two. May instruct MS 110 to change to state 304, which is set to one. Sooner or later, after the MS 110 begins to move and the same sequence of TPC commands is established, the BS 100 has the PCA set to one. Instructs MS 110 to change to state 306, which is set to one.

This process is summarized in the flowchart of FIG. This process begins at step 402, after which BS 100 analyzes the sequence of transmitted TPC commands at step 404. Then, in step 406, BS 100 determines whether the PCA and the PCA are based on this statistical analysis. The appropriate setting for the parameter is determined and, in step 408, the setting is passed to the MS 110 as one or more instructions instructing the MS 110 to change its setting. The process then loops back to the analysis at step 404 and continues to cycle while the connection between BS 100 and MS 110 remains active.

Although the setting of power control parameters according to the speed of the MS 110 is generally not appropriate, if recognition of the MS 110 speed is available, it can be used in connection with the SIR measurement to set the power control parameters. In some situations, it may even be appropriate to set parameters only according to speed. A simulation similar to that performed to determine the optimal power control step size for FIG. 2 is performed to determine the appropriate settings for the MS 110 moving at various speeds. As a result, a suitable setting is as follows:

Speed (km / h) PCA <2 One 2 2-30 One One 30-80 2 One > 80 One 2

The above description is PCA and It is directed to a BS (100) for determining appropriate settings for a parameter. Indeed, the setting of the parameter value may be, for example, "node B" which is part of a fixed infrastructure directly interfacing with the MS 110, or more in a Radio Network Controller (RNC). At a high level it can be the responsibility of various parts of a fixed infrastructure. Therefore, in this specification, the use of the terms "base station" or "first station", PCA and It should be understood to include the part of the network fixed infrastructure responsible for the determination and setting of parameter values.

The foregoing detailed description relates to a system for transmitting a power control command to the MS 110 separately from the instruction that the BS 100 sets the power control step size to the MS 110. However, the present invention is suitable for use within the scope of other systems. In particular, there is a variable power control step size and can be used in any system in which BS 100 instructs MS 110 to use a specific value for this step. Instead of instructing the MS 110 to use a particular step size, the step size to be used may also be determined by negotiation between the BS 100 and the MS 110.

Moreover, although the foregoing description relates to power control by the BS 100 of the uplink channel 124, such a method is equally well used for power control by the MS 110 of the downlink channel 122. Can be.

By reading this specification, other variations will be apparent to those skilled in the art. Such modifications may include other features that are already known in the design, manufacture, and use of radio communication systems and their components, and that may be used in place of or in addition to the features already described herein. Although the claims are formulated for a particular combination of features herein, the scope of the disclosure herein also includes any new feature or any new combination of features disclosed explicitly or implicitly herein, or a generalization thereof. It is to be understood that the present invention includes, without regard to whether or not it relates to the same invention as claimed in any claim and whether or not to alleviate some or all of the same technical problems solved by the present invention. Applicants should therefore note that new claims may be formed of such features and / or combinations of features during the performance of this specification or any further application derived herein.

In the specification and claims, the elements described in the singular do not exclude the presence of a plurality of such elements. Moreover, the word "comprising" does not exclude the presence of other elements or steps than those written.

The invention is applicable to a range of radio communication systems, for example UMTS.

Claims (12)

A communication channel is provided between the first station and the second station for transmitting information from one of the first station and the second station (sending station) to another station (receiving station), the transmitting station having a plurality of different ratios; A radio communication system, comprising means for adjusting its output power at a rate, The receiving station includes means for determining how the transmission strength of a signal received from the transmitting station should be adjusted, and sending a power control command to the transmitting station to instruct the transmitting station to adjust its output power. Means for determining an appropriate rate of adjustment of the output power of the transmitting station from the sequence of power control commands sent to the transmitting station, and means for conveying the rate of adjustment to the transmitting station; Is provided with means for responding to a communication from the receiving station to set an adjustment rate of its output power. The radio communication system according to claim 1, wherein the determination of an appropriate adjustment rate of the output power of the transmitting station also takes into account the average change in its output power over a predetermined period of time. A first station for use in a radio communication system having a communication channel between a first station and a second station, the second station having means for adjusting its output power at a plurality of different speeds, Means for determining how the transmission strength of a signal received from the second station should be adjusted, and means for transmitting a power control command to the second station to instruct the second station to adjust its output power. And means for determining an appropriate rate of adjustment of the output power of the second station from the sequence of power control commands sent to the second station, and means for delivering the rate of adjustment to the second station. Bureau. 4. The first station of claim 3, wherein the determination of an appropriate adjustment rate of the output power of the second station also takes into account the average change in its output power over a predetermined period of time. 4. The method of claim 3, wherein the determination of an appropriate adjustment rate of the output power of the second station also takes into account the time-weighted average change in its output power over a predetermined period of time. 1 branch office. 6. The apparatus according to any one of claims 3 to 5, wherein the means for determining the speed of the second station and the means for adjusting the determined appropriate adjustment rate of the output power of the second station according to the speed of the second station. A first station, characterized in that provided. As a second station, for use in a radio communication system having a communication channel between a second station and a first station, the first station has means for adjusting its output power at a plurality of different rates. Means for determining how the transmission strength of a signal received from the first station should be adjusted, and means for transmitting a power control command to the first station to instruct the first station to adjust its output power. And means for determining an appropriate rate of adjustment of the output power of the first station from the sequence of power control commands sent to the first station, and means for delivering the rate of adjustment to the first station. Bureau. 8. The second station of claim 7, wherein the determination of an appropriate adjustment rate of the output power of the first station also takes into account the average change in its output power over a predetermined period of time. 8. The second station of claim 7, wherein the determination of an appropriate adjustment rate of the output power of the first station also takes into account the time-weighted average change in its output power over a predetermined period of time. A communication channel is provided between the first station and the second station for transmitting information from one of the first station and the second station (the sending station) to the other station (the receiving station), and the transmitting station has a plurality of different ratios. As an operation method of the radio communication system which can adjust the output power of the furnace itself, Determining, by the receiving station, how the strength of the signal received from the transmitting station should be adjusted; Sending a power control command to the transmitting station to instruct the transmitting station to adjust its output power; Determining an appropriate rate of adjustment of the output power of the transmitting station from the sequence of power control commands sent to the transmitting station; Delivering the adjustment rate to the transmitting station; In response, the transmitting station sets an adjustment rate of its output power. Including a method of operating a radio communication system. 11. The method of claim 10, wherein the determination of an appropriate adjustment rate of the output power of the transmitting station also takes into account the average change in its output power over a predetermined period, the average change being repeated after each transmission of the power control command. And calculated and updated. 11. The method of claim 10, wherein the determination of an appropriate adjustment rate of the output power of the transmitting station also takes into account the time-weighted average change in its output power over a predetermined period, the average change being after each transmission of the power control command. Characterized in that it is calculated and updated iteratively.